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Reproductive System

Male reproductive system

The male reproductive system is basically divided into three. The primary sex organs, secondary sex organs, and the accessory organs. The primary sex organs consist of the testes, the secondary sex organs consist of the scrotal sac, the urethra, and the penis. The accessory organs are the prostrate glands, seminal vesicles and cowpers gland. They add secretion known as seminal fluid to the sperm to aid mobility. The seminal fluids and the sperm make up what we call semen.

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Male reproductive system

Testes: These are oval shaped organs present in the lower part of the abdomen. They are suspended in the body by the spermatic cords and are protected by a sac called scrotal sac or the scrotum. The scrotum regulates the temperature of the testes slightly below the body temperature of the sperm production (spermatogenesis). Outside each testis, is a highly coiled structure called epididymis where the sperm cells are temporarily stored.

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Spermatozoa of a male animal

Food is provided for the developing spermatozoa at the epididymis, which is connected to the vas deferens (sperm duct). The vas deferens is responsible for conducting sperm through the urethra to the base of the penis. The penis is an erective organ used in introducing the spermatozoa into the vagina. The penis like the urethra is a urinogenital organ. It consists of arteries and veins, through which when the animal is sexually stimulated, blood is pumped into the erective tissue of the penis giving it a turgid nature of carrying out copulation effectively. Note that copulation refers to the mating between the male and the female animals, whereas ejaculation is the release of sperm during copulation.

The male reproductive system in poultry is similar to that of mammals with just slight modifications. It consist of the testes, epididymis, papillae which is used in introducing the sperm into the virgina of the female and the cloaca which is a pathway for spermatozoa and faeces disposal.

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Male reproductive organ of a farm animal

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Male reproductive organ of a bird

The female reproductive system

Like in male, the female reproductive system consist of the primary sex character, the secondary sex character and the accessories.
The primary organs are the two ovaries; the secondary organs consist of the oviduct, uterus, cervix, vagina, clitoris and the vulva, while the accessory organs are made up of cowper’s and perineal glands. The ovaries are located in the abdominal region just below the kidney. They are responsible for egg formation (oogenisis) as well as produce female sex hormones which aid the development of female secondary sexual characteristics. A mature ovary is made up of germ cells which give rise to egg cells or ova. When these ova grow, they are surrounded by a cavity filled with fluid called Graafian follicle. When these follicles mature, they burst out and are released to the oviduct of the fallopian tube in a process called ovulation. The oviduct which consist of muscular walls leads to the uterus (womb) implantation and the whole period of pregnancy takes place in the uterus. The uterus opens into the vagina through the cervix. The cervix prevents anti-bodies from entering the womb. The vestibule opens to the exterior through the vulva which has in its front a small sensitive rod-like structure called the clitoris.

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Urinogenital system of a female rabbit

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The female reproductive organ

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Female reproductive system of a bird

The process of egg formation
The formation or synthesis of egg occurs partly in the ovary and partly in the oviduct, and is stimulated by hormones. The yolk is formed in the ovary and it is released from the ovary to the infundibulum or oviduct under the influence of luteinising hormone. Fertilization of the eggs takes place here.

The egg spends 15 minutes in the infundibulum and then moves to the magnum where it spends about 3 hours. During these periods, the albumen (a thick white material called the chalaza) is deposited round the egg.

From here, it moves down to the isthmus where it stays for about 1 hour 15 minutes. This is where the two shell membranes are put on the egg. The egg also takes it shape from here because the shape of the egg depends on the diameter of the isthmus. If the diameter of the isthmus is large, it will produce large eggs and if the diameter is small, it will produce small and slender eggs. The egg again moves down to the uterus or shell gland and stays here for about 18-20 hours. At this region, the formation of the albumen continues, the shell is also formed, the colour and the normal egg shape, are assumed. The egg finally passes down through the sphincter muscle to the vagina where it stays for only 10 minutes and is finally laid out through the cloaca.

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Egg of a domestic fowl showing external features

Animal Reproduction

Oestrus cycle

Heat period (Oestrus): This describes the period or time of sexual acceptability by female i.e the period marks the willingness of a female animal to accept a male animal for mating.

Heat period is characterised by the following signs:
(i) Swollen and reddened vulva.
(ii) Restlessness and undue noise making.
(iii) Loss of appetite.
(iv) Mucous discharge from the vagina.
(v) Mounting of other animals and allowing other animals to mount on them.
(vi) Waxing of tail vigorously.
(vii) Abnormal high temperature.

Heat period duration
The time an animal spends in heat varies from species to species.

Factors affecting heat period

Food – Adequate feeding therefore ensure times and regular heat periods.
Light – Follicle stimulating hormones (FSH) which influence egg production is influenced by light.
Temperature – High temperature delays heat as it causes a lot of stress on the animal.
Disease – Sick animals exhibit irregular heat periods.

Oestrus cycle therefore, is the period from the beginning of one heat (oestrus) period to the beginning of the next. It could also be said to be the period from the end of one oestrus (heat) to the end of another.

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Mating

This is also known as coition; whereby, the male penis is inserted into the female vagina with the ejaculation of sperm into the female genital organ, for fertilisation to take place. This is done on realisation that a female animal is on heat.

For mating to take place, the nerve ending at the tip of the penis is stimulated and set in motion. Thus making it become erect and turgid to guarantee copulation. This is made possible through the activities of the hormone testosterone.

There are different types of mating, they include:

(i) Pen mating
(ii) Flock or herd mating
(iii) Stud mating
(iv) Artificial insemination

Pen mating
Here, a limited number of female animals are given to a male animal, say about one male to 18 females. This method has the advantage of avoiding heat period loss but it could encourage the spread of veneral diseases. Similarly, when two female animals are on heat at the same time, one can be mated at a time by the male.

Flock mating
This occurs mostly in the extensive system of management where both male and female animals are allowed to move together in a range and mate themselves. One advantage of this method is widespread. The major disadvantage of this method is that one female can be mated by more than one male thus making it difficult to determine the father of the offspring. Already pregnant females may be remounted by the male and this may lead to miscarriage.

Stud mating
This is the type of mating whereby the male with desirable character is kept separately in a stud and any female on heat is led to it for mating, thereafter the female is removed from the stud. It is expected that the proven traits in the male can be transmitted to upgrade a herd as only male with proven qualities are used, while the cost of housing, feeding and maintenance of the male will be high.

Artificial insemination
This is the collection of semen from a male animal and artificially introducing it into the female reproductive tract.

The sperm or semen are collected by means of a teaser and stored in a refrigerator with liquid nitrogen at a temperature of about – 195 degree Celsius.

Advantages of artificial insemination

The following are advantages of artificial insemination:

(i) It is cost effective as the cost of maintaining a male animal is eliminated.
(ii) The mating of females that would not have been possible if we were to use the individual male animal due to the size of the female or may be because the female is ugly.
(iii) Offspring can be raised from a dead animal several years after the death of a male as semen can be collected and be stored for a very long time in a refrigerator.
(iv) Semen of animals with desirable character can be imported to service local breeds instead of importing an exotic male animal with its attendant high cost.
(v) Many females can be fertilised by semen from one male.
(vi) The spread of veneral disease is reduced, as physical contact of the animals is not there.

Disadvantages of artificial insemination
Given the erratic nature of electricity in Nigeria, it is doubtful if artificial insemination programme can be successful. Worst still is the fact that it requires a well trained personnel to carry it out. It cannot be done by just anybody.

Fertilisation
This is the union of the male and the female gametes to form a zygote. It takes place in the oviduct or fallopian tube of the female reproductive tract. After fertilisation, the zygote formed divides several times and it is transported down the oviduct where it gets attached to the placenta (implantation). The attached zygote now called foetus is attached to the placenta by the umbilical cord.

Gestation period
This is the period from fertilisation of the ovum to the process of giving birth (parturition). It is a period in pregnancy which results from successful mating. During this period, the young one passes through several stages. Gestation period varies greatly from species to species in farm animals.

Rat – 21 days
Rabbit – 31 days
Guinea pig – 67 days
Pig – 114-116 days
Cow – 280-286 days
Sheep – 145-150 days
Horse – 236 days
Dog – 63 days
Goat – 150 days

Gestation is controlled by the activities of the hormone progesterone and it ends with the secretion of oxytocin which initiates parturition.

Parturition
This is the act of giving birth in animals. It marks the end of gestation (pregnancy). It begins with the contraction of the uterine walls which causes the cervix to dilate, thus allowing the foetus to pass through it to the vagina along with the ruptured water bag. Parts of the umbilical cord as well as the placenta (after birth) follows the foetus almost immediately. Parturition is called by different names in different farm animals.

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Signs of approaching parturition

(i)   Swollen and soft vulva which may secrete a milky mucous discharge.
(ii) Restlessness and general pains.
(iii) The tail end or head becomes depressed.
(iv) Dropping of belly.
(v) The animal urinates often.
(vi) In the cow, the abdominal walls get relaxed.
(vii) The udder is distended and teat rich in milk.
(viii) In the rabbit, the fur is pulled out to make nest.

Equipment used in dairy farms

Feed and water trough, milking machine, buckets, weighing scale, ropes, milking chute, health and medical tools, cheese cloth, forage harvester and drugers, baler, silage fork, burdizzor pliers, milk test cup, auger, loading ramp/chute, etc.

Lactation

This is a period after parturition during which the female animal releases milk from its udder. At maturity, the mammary gland becomes mature and is responsible for milk production. Milk production which is of two parts is controlled by two different hormones, the first part which is milk secretion by the alveoli is controlled by the hormone progesterone while the second part, which is the milk-let-down is controlled by oxytocin.

The mammary gland (udder) consists of the alveoli, ducts, gland cistern, sinus and the teat canal. The milk which is secreted from the alveoli is conducted through the ducts to the gland or the sinus and to the leaf canal where milk is released. Milk-let-down can be stimulated by pressure applied to the teat by the young ones, by hand or mechanically by the use of milking machine. The sphincter muscle prevents the free flow of milk outside. Fresh milk is made fit for human consumption by a process known as pasteurisation, where the milk is exposed to a temperature of 71.7 degree Celsius for about 15 seconds to destroy harmful bacteria while still maintaining the nutritional value of the milk.

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(i) Udder or mammary gland of a cow

 

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(ii)a. Udder showing internal structure (longitudinal section)

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(ii)b.

Colostrum

This is the first milk produced by the udder after parturition. It is important that new born animals take colostrums because of the following qualities it possesses:

(i) It contains antibodies against diseases from where the newborn animal derives its immunity until when it can develop its own immunity.
(ii) It is highly digestible and has a laxative effect in the first few days. Colostrums last for the first four to six days after parturition.

The number of glands varies with species e.g.

Cattle (cow) – Four
Sheep (Ewe)  – Two
Goat (Doe)   – Two
Horse (Mare) – Two lines of twelve to fourteen
Rabbit (Doe) – Two lines of twelve to fourteen

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